Compact swirl augmented afterburners for gas turbine engines

ABSTRACT

An afterburner apparatus that utilizes a novel swirl generator for rapidly and efficiently atomizing, vaporizing, as necessary, and mixing a fuel into an oxidant. The swirl generator converts an oxidant flow into a turbulent, three-dimensional flowfield into which the fuel is introduced. The swirl generator effects a toroidal outer recirculation zone and a central recirculation zone, which is positioned within the outer recirculation zone. These recirculation zones are configured in a backward-flowing manner that carries heat and combustion byproducts upstream where they are employed to continuously ignite a combustible fuel/oxidizer mixture in adjacent shear layers. The recirculation zones accelerate flame propagation to allow afterburning to be completed in a relatively short length. Inherent with this swirl afterburner concept are design compactness, light weight, lower cost, smooth and efficient combustion, high thrust output, wide flammability limits, continuous operation at stoichiometric fuel/oxidizer mixture ratios, no combustion instabilities, and relatively low pressure losses.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.10/243,961, filed Sep. 13, 2002 and now U.S. Pat. No. 6,820,411 entitled“Compact, Lightweight High-Performance Lift Thruster IncorporatingSwirl-Augmented Oxidizer/Fuel Injection Mixing and Combustion”. Otherfeatures of the present invention are discussed and claimed in copendingU.S. application Ser. No. 10/360,469 entitled “Compact LightweightRamjet Engines Incorporating Swirl Augmented Combustion With ImprovedPerformance and in copending U.S. application Ser. No. 10/360,168entitled “Combined Cycle Engines Incorporating Swirl AugmentedCombustion for Reduced Volume and Weight and Improved Performance”.

FIELD OF THE INVENTION

The present invention generally relates to improvements in afterburnersand more particularly to an afterburner having an improved fuel/oxidizermixing and combustion apparatus, while being shorter, lighter and lowerin cost.

BACKGROUND OF THE INVENTION

Due to hot-structure temperature limitations, conventional gas turbineengines for fixed wing military aircraft are typically unable to fuelthe combustor to stoichiometric fuel/air mixture ratios which results inconsiderably lower thrust output, and the hot gas exhaust leaving theseengines contain large amounts of unused oxygen. Afterburners, not beingtemperature restricted, are employed to capitalize on the unspent oxygenby burning additionally injected fuel therein, thereby permitting thepilot to selectively generate additional thrust. The additional thrustcapacity is typically required for take-off, brief periods ofacceleration, supersonic flight and/or critical combat maneuvers.

Conventional afterburners typically include a diffuser, which slows downthe hot exhaust gases leaving the gas turbine engine, and a plurality ofspray rings or tubes which inject fuel into the passing oxygen-richexhaust gases. Mixing of the afterburner-injected fuel and the hotexhaust gases is accomplished by high-pressure injection, penetrationand atomization. A spark igniter or other suitable ignition source isemployed to initiate combustion of the afterburner mixture, whilebluff-body flameholders, such as V-shaped gutters that are mountedconcentrically around or downstream of a tail cone portion of thediffuser, and their wakes stabilize the flame and sustainself-propagating afterburner combustion. The afterburner diameter isexpanded, but not exceeding the main engine diameter, to mitigate thrustloss by decelerating the hot exhaust gases. A variable area nozzle isemployed to maximize thrust output for both the lower-temperatureexhaust during non-afterburning operation and the high-temperatureexhaust during afterburning operation.

As is well known in the art, the capability to afterburn approximatelydoubles the length of a gas turbine engine and entails a substantialweight penalty. While the weight and packaging issues of an afterburnerequipped gas turbine engine are relatively smaller than a turbojet orturbofan engine having a comparable thrust output, there is a need inthe art for a relatively more compact and fuel efficient afterburnerarrangement.

SUMMARY OF THE INVENTION

In one preferred form, the present invention provides an engine assemblyhaving a gas turbine engine and an afterburner apparatus. Theafterburner apparatus is coupled to the gas turbine engine and includesa burner and a swirl generator. The swirl generator has an inlethousing, a swirl vane pack, a centerbody assembly, and a plurality offuel injectors. The inlet housing is coupled to the inlet of the burnerand defines a hollow interior volume that serves as a conduit throughwhich at least a portion of the hot exhaust flow is conducted. Thehollow interior volume intersects the burner inlet at a dump stepwherein the afterburner housing has an inner dimension that is largerthan that of the inlet. The swirl vane pack is disposed within thehollow interior volume and has a plurality of vanes that cooperate tochange the velocity of the exhaust flow so that its velocity includes asubstantial tangential velocity component. The centerbody assembly iscoupled to the swirl vane pack and extends rearwardly therefrom. Theplurality of fuel injectors are coupled to at least one of the inlethousing, the swirl vane pack and the centerbody assembly and dispensethe fuel therefrom. The swirl generator converts the oxygen-rich, hotcore engine exhaust into a swirling, three-dimensional flowfield, afirst portion of which flows over the dump step to form an outerrecirculation zone and a second portion of the flowfield forms a centralrecirculation zone that is anchored by an aft end of the centerbodyassembly. A first portion of the fuel mixes with the first portion ofthe flowfield to fuel the outer recirculation zone, a second portion ofthe fuel mixes with the second portion of the flowfield to fuel thecentral recirculation zone, while the majority of the injected fuelfeeds the respective shear layers and the non-recirculating coreflowfield.

The afterburner apparatus of the present invention overcomes theaforementioned drawbacks through the use of a novel swirl generator thatpromotes rapid and efficient atomization and mixing of the fuel and thehot oxygen-rich exhaust gases. Self sustained ignition and efficientflame propagation is provided by the highly energetic recirculationzones coupled to the core flow through the high, swirl induced,turbulence in the shear layers that promotes very rapid combustion ofthe core flowfield mixture. Combustion can be completed in as little asone-fourth the length required in known afterburner devices.

Accordingly, the afterburner apparatus of the present invention isrelatively shorter, lighter in weight and more fuel efficient than theknown afterburner devices. No aero-intrusive instream flameholders arerequired, because the flame stabilization and propagation processes arecontrolled by the turbulence induced by the aerodynamics of the swirlingflowfield. No aero-intrusive fuel injection rings are needed either,because the fuel is injected from the trailing edges of the swirl vanesand the centerbody. The long tail cone is eliminated and replaced with ashort centerbody having an extendable and retractable tapered cone, andvariable angle swirl vanes to accommodate afterburning andnonafterburning modes of operation to maximize thrust output at allflight conditions.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional advantages and features of the present invention will becomeapparent from the subsequent description and the appended claims, takenin conjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view of a jet aircraft having a pair of liftthrust augmentors constructed in accordance with the teachings of thepresent invention;

FIG. 2 is a schematic illustration of a portion of the jet aircraft ofFIG. 1;

FIG. 3 is a cut-away perspective view of a portion of the lift thrustaugmentor illustrated in FIG. 1;

FIG. 4 is a longitudinal section view of a portion of the lift thrustaugmentor;

FIG. 5 is an exploded perspective view of a portion of the lift thrustaugmentor illustrating the elbow in greater detail;

FIG. 6 is a longitudinal section view of the elbow;

FIG. 7 is an exploded perspective view of a portion of the lift thrustaugmentor;

FIG. 8 is an exploded perspective view of a portion of the lift thrustaugmentor illustrating the centerbody hub assembly in greater detail;

FIG. 9 is a longitudinal section view of the centerbody hub assembly;

FIG. 9A is a schematic view of the swirl generator of the presentinvention illustrating several various centerbody assembly and wallinjector fueling schemes;

FIG. 10 is a perspective view of a portion of the swirl generatorillustrating the swirl vane pack in greater detail;

FIG. 10A is a partial top plan view of an alternately constructed swirlvane pack illustrating a profiled vane configuration;

FIG. 11 is an exploded perspective view of the swirl vane pack of FIG.10;

FIG. 12 is an exploded sectional view of a portion of the swirl vanepack;

FIG. 13 is a longitudinal section view similar to that of FIG. 4 butillustrating a combustion event;

FIG. 14 is a partially broken away perspective view of a portion of aswirl generator constructed in accordance with the teachings of analternate embodiment of the present invention;

FIG. 15 is a sectional view of a portion of a swirl generatorconstructed in accordance with the teachings of a second alternateembodiment of the present invention which illustrates an alternativelyconstructed centerbody hub assembly in detail;

FIG. 16 is an exploded perspective view of a portion of a swirlgenerator constructed in accordance with the teachings of a thirdalternate embodiment of the present invention which illustrates anotheralternatively constructed centerbody hub assembly;

FIG. 17 is a longitudinal section view of the centerbody hub assembly ofFIG. 16;

FIG. 18 is a partially broken away side elevation view of a swirlgenerator constructed in accordance with the teachings of a fourthalternate embodiment of the present invention;

FIG. 19 is a perspective view of a portion of a swirl generatorconstructed in accordance with the teachings of a fifth alternativeembodiment of the present invention which illustrates a vane for analternative swirl vane pack with a plurality of fuel injection sites;

FIG. 20 is a partial sectional view of the vane of FIG. 19;

FIG. 21 is a perspective view of a portion of a swirl generatorconstructed in accordance with the teachings of a sixth alternativeembodiment of the present invention which illustrates a vane for analternative swirl vane pack with turbulator ramps and a plurality offuel injection sites;

FIG. 22 is a partial sectional view taken through the vane of FIG. 21;

FIG. 23 is a front elevation view of a swirl generator constructed inaccordance with the teachings of a seventh alternative embodiment of thepresent invention which illustrates a vane for a third alternative swirlvane pack having scallops;

FIG. 24 is a partial sectional view of a swirl generator constructed inaccordance with the teachings of a eighth alternative embodiment of thepresent invention which illustrates an alternative inlet housing whereina plurality of channels are formed into the inlet ramp;

FIG. 24A is a sectional view taken along the line 24A—24A of FIG. 24;

FIG. 25 is a partial sectional view of a swirl generator constructed inaccordance with the teachings of a ninth alternative embodiment of thepresent invention which illustrates another alternative inlet housingillustrating the incorporation of fuel injection sites into the inletramp;

FIG. 26 is a partial sectional view of a swirl generator constructed inaccordance with the teachings of a tenth alternative embodiment of thepresent invention which illustrates an alternative combustorillustrating the use of a quarl extension;

FIG. 27 is a partial sectional view of a swirl generator constructed inaccordance with the teachings of a eleventh alternative embodiment ofthe present invention which illustrates another alternately configuredcenterbody hub assembly;

FIG. 28 is a partial sectional view of a swirl generator constructed inaccordance with the teachings of a twelfth alternative embodiment of thepresent invention which illustrates another alternately configuredcenterbody hub assembly;

FIG. 29 is a front elevation view of a ramjet missile that incorporatesa swirl generator constructed in accordance with the teachings of thepresent invention;

FIG. 30 is a longitudinal section view taken along the line 30—30 ofFIG. 29;

FIG. 30A is a view similar to FIG. 30 but illustrating a swirl generatorthat employs flow guide vanes;

FIG. 31 is a longitudinal section view of a ramshell that incorporates aswirl generator constructed in accordance with the teachings of thepresent invention;

FIG. 32 is a partial longitudinal section view of a combined cycleengine having a plurality of ramjet engines that incorporate a swirlgenerator constructed in accordance with the teachings of the presentinvention;

FIG. 33 is a section view taken along the line 33—33 of FIG. 32;

FIG. 34 is a partial longitudinal section view of a second combinedcycle engine having a plurality of ramjet engines that incorporate aswirl generator constructed in accordance with the teachings of thepresent invention;

FIG. 35 is a section view taken along the line 35—35 of FIG. 34;

FIG. 35A is a partial longitudinal section view similar of a thirdcombined cycle engine having a ramjet engine that incorporates a swirlgenerator constructed in accordance with the teachings of the presentinvention;

FIG. 36 is a longitudinal section view of a rocket-based combined cycleengine constructed in accordance with the teachings of the presentinvention;

FIG. 37 is a rear elevation view of the rocket-based combined cycleengine of FIG. 37;

FIG. 38 is a perspective view of a portion of the rocket-based combinedcycle engine illustrating the variable area throat in an open condition;

FIG. 39 is a perspective view similar to that of FIG. 38, butillustrating the variable area throat in a closed condition;

FIG. 40 is a longitudinal section view of an aircraft engine having aconventional afterburner;

FIG. 41 is a longitudinal section view similar to FIG. 40 butillustrating an afterburner that incorporates a swirl generatorconstructed in accordance with the teachings of the present invention;and

FIG. 41A is a longitudinal section view similar to that of FIG. 41 butillustrating an afterburner that utilizes a swirl generator with acollapisable centerbody cone.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1 of the drawings, an exemplary jet aircraft 8 isillustrated to include a pair of lift thrust augmentors 10 that areconstructed in accordance with the teachings of the present invention. Aconventional gas turbine engine 12 serves as the primary source ofpropulsive power for the jet aircraft 8, while the lift thrustaugmentors 10 are selectively operable to produce thrust when the demandfor thrust exceeds a predetermined threshold.

With additional reference to FIGS. 2 through 4, each lift thrustaugmentor 10 includes an air delivery portion 20, a swirl generator 30and a combustor/nozzle portion 40. When combined, the swirl generator 30and combustor/nozzle portion 40 are also known as a compactswirl-augmented thruster (COSAT). The air delivery portion 20 includes abutterfly valve 50 and in the particular example provided, an elbow 60.It will be readily apparent to those skilled in the art that the airdelivery portion 20 may be configured in any manner to package the liftthrust augmentor 10 into a particular application and as such, the elbow60 may be omitted or the bend angle changed to suit the specific needsof a given application.

The butterfly valve 50 and the elbow 60 are coupled in fluid connectionto the gas turbine engine 12. More specifically, hot high-pressure airis bled from the bypass fan 12 a of the gas turbine engine 12 anddiverted through a lateral jetscreen feed system (not specificallyshown) to an attitude control system 70. The butterfly valve 50, whichis normally maintained in a closed condition and coupled in fluidconnection with the attitude control system 70, is opened to divert apredetermined amount (i.e., mass flow rate) of the hot high-pressurebleed air to the lift thrust augmentors 10. In the particular embodimentprovided, about 30% of the airflow that is directed into the attitudecontrol system 70 is redirected to the lift thrust augmentors 10 whenthe lift thrust augmentors 10 are operated to provide maximum thrust.

The air that passes by the butterfly valve 50 is routed through theelbow 60 to the swirl generator 30. As will be described in greaterdetail below, the swirl generator 30 injects fuel in to the air andpromotes the efficient mixing of the air and fuel. A torch igniter 80,such as that described in copending U.S. patent application Ser. No.10/217,972 entitled “Torch Igniter”, the disclosure of which is herebyincorporated by reference as if fully set forth herein, is employed toinitiate a combustion event wherein the fuel/air mixture is burned inthe combustor 40 a of the combustor/nozzle portion 40. Those skilled inthe art will appreciate that igniters, including electric sparkigniters, plasma jet igniters, lasers and microwaves, may be employed inthe alternative. As the construction of the combustor 40 a is well knownin the art, a detailed discussion of the combustor will not be providedherein. For example, those skilled in the art will appreciate that thecombustor 40 a may be wholly formed of a suitable high temperaturematerial, or may utilize a perforated liner that facilitates air-coolingof the combustor 40 a, or may utilize a wall that is partially or whollycomprised of fluid conduits that facilitate a flow of fluid through orabout the combustor wall that operates to cool the combustor 40 a duringits operation.

Thereafter, hot combustion by-products are expelled through a nozzle 40b, such as a convergent nozzle (FIG. 4) or a convergent/divergent nozzle(FIG. 2), to produce thrust. It will be understood that the particularcombustible mixture (i.e., a liquid fuel and air) that is utilized inthis example is not intended to limit the scope of the disclosure in anyway. In this regard, those skilled in the art will understand that anytype of fuel (e.g., liquid, slurry, gas) and any type of oxidant (e.g.,air, hydrogen peroxide, oxygen) may be utilized in the swirl generatorand lift thrust augmentor of the present invention. Accordingly, whenthe term “mixing” is used in the context of a fuel/oxidant mixture, itwill be understood to include atomization and vaporization if the fuelis not injected in gaseous state.

With reference to FIGS. 5 and 6, the elbow 60 is illustrated to turn theairflow 90 about 90° and is relatively constant in its cross-sectionalarea. The elbow 60 includes an elbow housing 94, a plurality of flowguide vanes 96, a pair of side covers 98 and an aerodynamic fairing 100.As will be readily apparent to one skilled in the art, the components ofthe elbow 60 may be fabricated out of any appropriate material, theselection of which is largely dependant on the temperature of the airentering the air delivery portion 20 (FIG. 2). In the particular exampleprovided, the inlet temperature may be relatively high and as such,materials including Cress stainless steel series (e.g., 304, 321),Haynes 240, ceramic matrix composites (e.g., C/SiC, SiC/SiC, Si₃N₄,Al₂O₃/Al₂O₃) would be appropriate for the construction of the componentsof the elbow 60. As those skilled in the art will appreciate, variousthermally protective coatings (e.g., ceramics) and/or heat transfertechniques that rely on a cooling effect provided by a working fluid(e.g., fuel, air) may additionally or alternatively be employed torender the components of the elbow 60 suitable for a given set of inletconditions.

The elbow housing 94 is shown to include an inlet portion 102 and anoutlet portion 104 that are interconnected by an arcuate turning portion106. The elbow housing 94 may be unitarily formed via conventionalprocesses such as casting or machining (from bar stock), or may be amulti-component fabrication that is fixedly coupled together as bywelding. The lateral sidewalls 110 of the turning portion 106 include aplurality of concentric slots 112 that are formed therethrough, whilethe endwall 114 in the turning portion 106 includes a fairing aperture116. The fairing aperture 116 is sized to receive a portion of theaerodynamic fairing 100, as well as a conduit 120 (FIG. 4) that couplesthe swirl generator 30 to an ignition controller 122 (FIG. 4) thatactuates the lift thrust augmentor 10, as well as the fuel source 126(FIG. 4) of the jet aircraft 8.

The flow guide vanes 96 are curved about a single axis and slide intothe turning portion 106 through the concentric slots 112. Accordingly,the flow guide vanes 96 extend across the inner dimension of the turningportion 106 in a direction that is generally perpendicular to thedirection of the air flow and concentric with the radius of the turn inthe turning portion 106. The flow guide vanes 96 are also configuredsuch that they extend between the inlet portion 102 and the outletportion 104 of the elbow housing 94. Accordingly, the radially inwardflow guide vanes, such as flow guide vane 96 a, are relatively shorterthan the radially outer flow guide vanes, such as flow guide vane 96 d.

The leading and trailing edges 130 and 132, respectively, of the flowguide vanes 96 preferably engage the opposite ends of the concentricslots 112, while the opposite lateral sides 136 of the flow guide vanes96 are abutted against the side covers 98, which are fixedly secured tothe elbow housing 94 via a plurality of screws (not specifically shown).Additionally or alternatively, the flow guide vanes 96 may be welded inplace to secure them in place within the concentric slots 112.

The flow guide vanes 96 are employed to mitigate air flow distortionsand flow separation induced by the associated upstream butterfly valve50 (FIG. 2) as well as to prevent further flow separation, the creationof secondary flows and large scale profile distortions due tocentrifugal forces as the inlet flow undergoes the 90° turn through theturning portion 106. If unabated, secondary flows, separations anddistortions tend to complicate the design and operation of thedownstream fuel injection, alter the mixing effectiveness and providestimuli for combustion instabilities. Consequently, the configurationsof the air delivery portion 20 (generally) and the elbow 60(specifically) provide a high degree of uniformity in the flow of air(i.e., a uniform axial airflow) to the swirl generator 30.

As best seen in FIG. 6, the flow guide vanes 96 cooperate with the elbowhousing 94 to define a plurality of inlet flow channels 140. As the paththat is defined by inlet flow channel 140 a is relatively shorterbetween the inlet portion 102 and the outlet portion 104 as comparedwith the inlet flow channel 140 e and as transient flow differencesbetween the inlet flow channels 140 are highly undesirable, the flowguide vanes 96 of the particular embodiment illustrated are positionedin a radial direction in a manner that provides inlet flow channels 140with dissimilar cross-sectional areas such that the inlet flow channels140 produce a series of inlet flows that are relatively uniform in flowvelocity. Accordingly, the inlet flow 150 to the swirl generator 30 hasa velocity that is substantially completely defined by an axial velocitycomponent.

In FIGS. 4 through 6, the conduit 120 that couples the swirl generator30 to the ignition controller 122 (FIG. 2) and the fuel source 126 (FIG.2) is illustrated to extend through the endwall 114 of the turningportion 106, through a conduit aperture 154 in the flow guide vane 96 dand out the outlet portion 104 of the elbow housing 94 where it iscoupled to the swirl generator 30. The presence of the conduit 120 inthe interior of the turning portion 106 would ordinarily initiate a flowseparation, which as mentioned above, reduces the effectiveness andefficiency of the lift thrust augmentor 10. The aerodynamic fairing 100,however, is employed to reduce or eliminate altogether, the flowseparations that would be induced by the presence of the conduit 120.

In the example provided, the aerodynamic fairing 100 includes a hollowhub 156 and an airfoil portion 158 that is coupled to the hub 156. Theconduit 120 extends through the hollow interior of the hub 156 and maybe coupled thereto by any appropriate retaining means, including aninterference fit (e.g., shrink fit or press fit), brazing and welding.The airfoil portion 158, which surrounds the conduit 120, extends in thein the down-wind direction in a tapered manner and terminates at itstrailing edge 164 with a relatively small amount of trailing edgebluntness. Alternatively, the airfoil portion 158 may be configured toabut the windward side of the conduit 120. The airfoil portion 158 ispositioned within the flow channel 140 e so as to reduce or eliminatealtogether the flow separations that would be induced by the presence ofthe conduit 120. The hub 156 and/or airfoil portion 158 may be fixedlycoupled to the elbow housing 94 by any appropriate retaining means,including an interference fit (e.g., shrink fit or press fit), brazingand welding.

With reference to FIGS. 4 and 7, the swirl generator 30 is illustratedto include an inlet housing 200, a centerbody hub assembly 204, a swirlvane pack 206 and a wall injector assembly 208. In the particularexample provided, the inlet housing 200 is illustrated to include anupper inlet housing segment 200 a, which is coupled to and integrallyformed with the outlet portion 104 of the elbow 60, an optional wallinjection housing 228 (which will be described in detail, below) and anoptional lower inlet housing segment 200 b, which is coupled to thecombustor/nozzle portion 40 and which includes an inlet extension 210and an inlet ramp 212. Alternatively, the inlet housing 200 may beunitarily formed. Also alternatively, the upper inlet housing segment200 a may be separate from the outlet portion 104 of the elbow 60 and/orthe lower inlet housing segment 200 b, if included, may be integrallyformed with the combustor/nozzle portion 40. Accordingly, those skilledin the art will appreciate that one or more of the upper and lower inlethousing segments 200 a and 200 b and the wall injection housing 208 maynot exist as a discrete component. In the presently preferredconfiguration of the lift thrust augmentor 10, the upper inlet housingsegment 200 a is integrally formed with the elbow 60 so as to minimizethe overall length of the lift thrust augmentor 10.

The inlet housing 200 defines a hollow interior volume 220 into whichthe centerbody hub assembly 204 extends. The injection of fuel into thelift thrust augmentor 10 is illustrated to include fuel injectionthrough the wall 224 of the inlet housing 200 at a location forwardly ofthe inlet ramp 212. The sizing and purpose of the inlet ramp 212 will bediscussed in greater detail, below.

As all fuel injection occurs downstream of the swirl vane pack 206, thepresence of the inlet extension 210 effectively shifts the variouspoints of fuel injection in an upstream direction relative to the inletramp 212 so as to provide additional time for the fuel to mix (i.e., forthe liquid fuel of this example to atomize, mix and vaporize) prior toentering the combustor 40 a. Those skilled in the art will appreciatethat the amount of additional mixing time that is afforded by the inletextension 210 is a function of its length. Those skilled in the art willalso appreciate that the need for an inlet extension is based on thestate of the air flow, such as the velocity, temperature, pressure andthe characteristics of the fuel that is being used. Therefore, in someof the applications that we have conceived for the swirl generator 30,such as ramjets, the air flow is at a sufficiently high temperature suchthat even liquid fuels are rapidly mixed (i.e., atomized, mixed andvaporized), which permits the aft end of the centerbody hub assembly 204to be positioned so as to extend downstream of the inlet ramp 212 intothe combustor 40 a.

In the particular example provided, wall injection is accomplishedthrough the wall injector assembly 208. The wall injector assembly 208includes an annular wall injection housing 228 (which is considered tobe part of the injection housing 200) and a plurality of fuel injectors230 that are circumferentially spaced about the wall injection housing228. The inside diameter of the wall injection housing 228 is equal indiameter to the inner diameter of the lower inlet housing segment 200 bso as to be flush and not to induce flow separations, etc. that wouldtend to impede the efficiency of the swirl generator 30. The insidediameter wall injection housing 228, however, is somewhat smaller indiameter than the inside diameter of the upper inlet housing segment 200a for reasons that will be described in detail, below.

The wall injection housing 228 is disposed between the aft end of theupper inlet housing segment 200 a and the forward end of the lower inlethousing segment 200 b. Conventional Viton O-rings 238 or other sealingdevices that are well known in the art are employed to seal theinterface between the opposite faces of the wall injection housing 228and the upper and lower inlet housing segments 200 a and 200 b. Threadedfasteners (not shown) are employed to fixedly couple the elbow 60, theupper inlet housing segment 200 a, the wall injection housing 228, thelower inlet housing segment 200 b and the combustor/nozzle portion 40together.

In the example shown, the fuel injectors 230 comprise eight flush-mountsimplex fuel injectors such as Woodward FST Simplex Injectors, which arecommercially available from Woodward FST, Inc. of Zeeland, Mich. Thoseskilled in the art will appreciate, however, that other amounts and/ortypes of fuel injectors, including stand-off or wall flush simplex fuelinjectors, orifice injectors or variable area poppet fuel injectors withvariations in drop sizes and cone angles (i.e., solid or hollow cone)may also be used.

In FIGS. 7 through 9, the centerbody hub assembly 204 is illustrated toinclude the conduit 120 and a centerbody assembly 236, which includes aforward centerbody 240, a conduit retainer 242, and an aft centerbody244 and an igniter 246. In the particular embodiment illustrated, theigniter 246 is a conventional spark igniter which is commerciallyavailable from sources such as those that are manufactured by ChampionSpark Plug Company of Toledo, Ohio. Accordingly, a detailed descriptionof the construction of the igniter 246 will not be provided herein.Those skilled in the art will appreciate that other types of igniters,such as a plasma jet igniter (also well known in the art andcommercially available from sources such as Unison Industries Inc. ofJacksonville Fla.), microwave ignition devices, and laser ignitiondevices may be employed as an alternative to a spark igniter.

As noted above, the conduit 120 extends through the elbow 60 (FIG. 4) tocouple the swirl generator 30 (FIG. 4) to the ignition controller 122(FIG. 4) and the fuel source 126 (FIG. 4). In the particular embodimentprovided, the conduit 120 is a hollow tube into which an electricalcable 250 and a plurality of fuel conduits 252 are housed. Theelectrical cable 250 electrically couples the ignition controller 122 tothe igniter 246 such that electrical energy is transmitted to theigniter 246 when the ignition controller 122 is actuated to permit theigniter 246 to produce a discharge arc (not shown). The fuel conduits252 couple in fluid connection of the fuel source 126 to a plurality offuel injectors in the aft centerbody 244. Those skilled in the art willappreciate, however, that a single fuel conduit (not shown) may bealternatively employed, wherein the single fuel conduit supplies fuel toa fuel manifold within or coupled to the aft centerbody 244 to which arecoupled the fuel injectors. Also alternatively, the swirl generator 30may be constructed without a discrete fuel conduit 252 wherein suchfunction would additionally be provided by the conduit 120 that housesthe electrical cable 250. Those skilled in the art will appreciate thatthese fuel splits could alternatively be accomplished through a set oforifices that effectively limit the mass flow rate of fuel therethrough.

The forward centerbody 240 is a generally hollow structure having acentral aperture 270 into which the conduit 120 is fixedly coupled, asthrough brazing for example. The exterior surface of the forwardcenterbody 240 includes an aerodynamically contoured leading surface 272as well as a mounting flange 274 to which the swirl vane pack 206 ismounted. The aerodynamically contoured leading surface 272, which isillustrated to be generally spherically shaped in the particular exampleprovided, serves to guide the inlet flow 150 (FIG. 4) exiting the elbow60 radially outwardly around the forward centerbody 240 and into theswirl vane pack 206. The mounting flange 274 has a diameter that isgenerally smaller than the trailing edge of the aerodynamicallycontoured leading surface 272 to thereby create an abutting flange 278at the intersection of the mounting flange 274 and the leading surface272. The aft end of the interior of the forward centerbody 240 includesa counterbored portion 280 that is configured to receive the conduitretainer 242.

The conduit retainer 242 is an annular structure with an open centerthat is configured to receive therethrough portions of the igniter 246and the electrical cable 250. A plurality of conduit mounting apertures284 are formed through the conduit retainer 242 and are sized tomatingly receive an associated one of the fuel conduits 252. The fuelconduits 252 are preferably fixedly coupled to the conduit retainer 242in their associated conduit mounting apertures 284 through anappropriate joining process, such as brazing. Conventional threadedfasteners, such as socket head cap screws 290, are preferably employedto fixedly but releasably couple the conduit retainer 242 to the forwardcenterbody 240.

The aft centerbody 244 may be configured in several different manners tooptimize the efficiency of the lift thrust augmentor 10 and tailor itsthrust output to a desired thrust output level. In the particularexample provided the aft centerbody 244 includes first and secondinjector rings 300 and 302, respectfully, and an aft bluff boat-tail304.

A conventional Viton O-ring 310 or other well known sealing device isemployed to create a seal between the first injector ring 300 and theaft face of the forward centerbody 240. The first injector ring 300 hasa generally hollow center through which the igniter 246 is received, andan outside diameter that is relatively larger in diameter than that ofthe mounting flange 274. The first injector ring 300 is illustrated toinclude a plurality of circumferentially spaced apart fuel injectors320, such as simplex injectors having a flow number (FN) equal to about8.5, which are commercially available from Woodward FST, Inc. ofZeeland, Mich. Those skilled in the art, however, will appreciate thatother types of fuel injectors, including a plurality of orifices, couldbe additionally or alternatively employed. Although the injectors 320are illustrated as being configured to inject fuel in a radially outwarddirection, those skilled in the art will appreciate that the fuelinjectors 320 may be alternatively configured to inject fuel in anupstream direction, a downstream direction or any combination of theradially outward, downstream and upstream directions.

The fuel injectors 320 are coupled in fluid connection to a manifold 324that is formed into the first injector ring 300. In the exampleprovided, the manifold 324 is coupled in fluid connection to anassociated one of the fuel conduits 252 to receive fuel therefrom. Thoseskilled in the art will appreciate, however, that the manifold 324 couldalso be coupled in fluid connection to each of the fuel conduits 252. AViton O-ring 326 or other well known sealing device is employed to sealthe interface between the conduit retainer 242 and the front face of thefirst injector ring 300.

A conventional Viton O-ring 330 or other well known sealing device isemployed to create a seal between the second injector ring 302 and theaft face of the first injector ring 300. The second injector ring 302has a generally hollow center that is at least partially threaded so asto threadably engage a threaded portion 336 of the igniter 246 in aconventional manner. The second injector ring 302 may include no fuelinjectors (i.e., constitute a “blank” injector ring as shown in FIG.9A), or may include a plurality of circumferentially spaced fuelinjectors 340, such as simplex or orifice injectors, depending on thedesired output of the lift thrust augmentor 10. Although the injectors340 are illustrated as being configured to inject fuel in a radiallyoutward direction (FIG. 8), those skilled in the art will appreciatethat the fuel injectors 340 may be alternatively configured to injectfuel in an upstream direction, a downstream direction or any combinationof the radially outward, downstream and upstream directions.

The second injector ring 302 may be keyed or otherwise aligned to thefirst injector ring 300 in any conventional manner to maintain the firstand second injector rings 300 and 302 in a condition wherein they arealigned about a common axis. In this condition, the outer surface of thesecond injector ring 302 substantially coincides with the outer surfaceof the first injector ring 300 to thereby prevent the generation of anyflow separations or discontinuities.

In the embodiments wherein the second injector ring 302 includes fuelinjectors 340, a manifold 344, which is formed into the second injectorring 302, is employed to couple in fluid connection the fuel injectors340 to an associated fuel conduit 252. The manifold 344 may be coupledin fluid connection to the manifold 324 of the first injector ring 300,or to an aperture 345 that is formed through the first injector ring 300as is shown in FIG. 8. The interface between the first and secondinjector rings 300 and 302 is sealed by a Viton O-ring 346 in an areaproximate the aperture 345.

The aft bluff boat-tail 304 includes a flange portion 360 and aflow-effecting portion 362. The flange portion 360 abuts the aft face ofthe second injector ring 302 and includes a pair of apertures 364through which conventional socket head cap screws 366 are received. Thecap screws 366 extend through similar apertures formed in the first andsecond injector rings 300 and 302 and the conduit retainer 242 andthreadably engage apertures (not shown) in the forward centerbody 240 tofixedly couple these components to one another. The flange portion 360also includes a hollow center 370 into which a tip 246 a of the igniter246 extends. The hollow center 370 is chamfered on its aft end so as toprovide additional space about the tip 246 a for a flame kernel.

The flow-effecting portion 362 is coupled to the outer perimeter of theflange portion 360. In the particular embodiment provided, theflow-effecting portion 362 is frusto-conically shaped and includes aplurality of circumferentially spaced apart fuel injectors 380 that areconfigured to inject fuel in a predetermined direction. Like the secondinjector ring 302, the flow-effecting portion 362 may be alternatelyconfigured to include no fuel injectors (i.e., constituting a “blank”bluff body). Although the injectors 380 are illustrated as beingconfigured to inject fuel in an upstream direction, those skilled in theart will appreciate that the fuel injectors 380 may be alternativelyconfigured to inject fuel in a radially outward direction, a downstreamdirection or any combination of the radially outward, downstream andupstream directions.

In the example illustrated, the flow-effecting portion has an initialouter diameter that matches the outer diameter of the first and secondinjector rings 300 and 302. The flow-effecting portion 362 terminates atits aft end at a sharp edge 386 that operates to initiate flowseparation and to anchor and radially extend the central recirculationzone 610 (FIG. 13) to increase its size and flameholding capabilities.

Although the centerbody hub assembly 204 has been illustrated thus faras being formed from a plurality of discrete components, those skilledin the art will appreciate that various known manufacturing techniques,including direct metal fabrication, may be employed so as to reduce theactual number of components that are utilized. For example, the forwardcenterbody 240, the swirl vane pack 206 and the first injector ring 300may all be unitarily formed, which would thereby eliminate the need forthe conduit retainer 242.

Referring to FIG. 9A, the swirl generator 30 of the present invention isschematically illustrated to show several of the various fueling optionsthat may be employed. The fuel injectors 230 may comprise, for example,orifices A, flush-mount simplex injectors B or stand-off simplexinjectors C. The fuel injectors of the aft centerbody assembly 244(i.e., fuel injectors 320, 340, 380 and 840) may include simplexinjectors D or orifices E, or may be omitted in part (blank) asdesignated by reference letter F.

In FIGS. 4, and 10 through 12, the swirl vane pack 206 is illustrated toinclude a mounting hub 400, a plurality of vanes 402 and a shroud 404.In the particular example provided, the swirl vane pack 206 is anassembly wherein the components comprising the swirl vane pack 206 arefabricated, assembled and fixedly secured to one another. Those skilledin the art will appreciate, however, that alternative fabricationtechniques may be employed to reduce the number of components thatcomprise the swirl vane pack 206. For example, technologies such as hotisostatic pressing, casting and direct metal fabrication may be employedto form the swirl vane pack 206, either wholly or partially, or incombination with the centerbody assembly 236 or portions thereof asdescribed above.

The mounting hub 400 is an annular structure that is received over themounting flange 274 (FIG. 9) of the forward centerbody 240 (FIG. 9) injuxtaposed relation with the abutting flange 278 (FIG. 9) of the forwardcenterbody 240 and the front face of the first injector ring 300 (FIG.9). The cap screws 366 (FIG. 8) exert a clamping force that fixedly butremovably secures the aft centerbody 244 to the forward centerbody 240.As the mounting hub 400 abuts the mounting flange 274 and the front faceof the first injector ring 300, the clamping force is also transmittedbetween the abutting flange 278 and the front face of the first injectorring 300, which operates to fixedly secure (both axially and radially)the mounting hub 400 therebetween.

The vanes 402 of the swirl vane pack 206 are configured with a swirlnumber that ranges from about 0.4 to about 1.2 so as to permit thecombustor/nozzle portion 40 to achieve a combustor length-to-diameter(UD) ratio (as measured from a plane at which the dump step 636 in FIG.13 to the throat of the nozzle portion 40 b) that is less than about2.0, and preferably less than about 1.6 and more preferably about 1.0 orless. In the particular example provided, we utilized twelve vanes 402having a straight configuration that is skewed to the centerline of themounting hub 400 so as to provide a swirl number of 0.54. Those skilledin the art will appreciate that various other vane configurations mayalternatively be employed, including vanes with different skew anglesand/or an arcuate or helical profile (FIG. 10A). As the swirl vane pack206 is comprised of a plurality of discrete components, the vanes 402are configured with tabs 410 a and 410 b on their opposite ends. Theradially inward tabs 410 a are configured to engage apertures 412 thatare formed on the opposite faces of the mounting hub 400. The tabs 410 aand the apertures 412 cooperate to align the vanes 402 to the mountinghub 400 so that the vanes 402 may be coupled to the mounting hub 400 ina conventional manner, such as brazing or welding.

The shroud 404 includes a pair of end caps 420 and a pair ofcircumferentially extending portions 422. The end caps 420 include aplurality of apertures 424 that are configured to receive the radiallyoutward tabs 410 b on the vanes 402. In a manner similar to that of theapertures 412 of the mounting flange 274, the apertures 424 cooperate toalign the vanes 402 to the end caps 420. The circumferentially extendingportions 422 are disposed around the perimeter of the vanes 402 betweenthe tabs 410 b and the end caps 420, circumferentially extendingportions 422 and vanes 402 are fixedly secured together, as throughwelding.

With reference to FIG. 4, the swirl vane pack 206 is illustrated to befixedly coupled to the centerbody hub assembly 204 in the mannerdescribed above and disposed between the wall injector assembly 208 anda recessed step 500 formed in the upper inlet housing segment 200 a. Inthis location, the trailing edges of the vanes 402 of the swirl vanepack 206 are located upstream of all fuel injection sites, whicheliminates any potential for flashback which would damage the vanes 402.The shroud 404 of the swirl vane pack 206 is preferably sized to engagein a press-fit manner the recessed step 500 in the lower inlet housingsegment 200 b to thereby structurally couple the swirl vane pack 206 andthe centerbody hub assembly 204 to the inlet housing 200.

The swirl generator 30 is configured such that the vanes 402 imparttangential velocities to the axial inlet flow 150 to convert the inletflow 150 into a spiraling, three dimensional swirling flow structure orflowfield 510 (FIG. 4). The flowfield 510 has a dramatic effect on therate of fuel mixing, atomization, droplet vaporization, flamepropagation, combustion efficiency, combustion stability, combustionintensity and widens flammability limits. Those whom are skilled in theart will appreciate that radial velocities will be affected by theswirling effect, but that the major impact of swirling effect concernsthe aforementioned tangential velocity component.

With reference to FIG. 13, the high tangential velocities produced bythe vanes 402, whether straight or profiled in their configuration,creates a very intense shear layer 600 and enhances the large scalevortex or central recirculation zone 610 that is generated and anchoredby the bluff end 614 of the aft centerbody 244, even at relatively lowlevels of swirl (i.e., a level of swirl that is greater than or equal toabout 0.4). In the case of vanes 402 having a flat configuration,especially high shear stresses are created that promote very efficientmixing of the fuel that is introduced into the inlet housing 200 via thewall injector assembly 208 and the injectors 320, 340 and 380 in the aftcenterbody 244 due to high intensity turbulence that is generated by thetrailing edge vortices that are induced by the flow separation on thelee side of the vanes 402. Combustion in the central recirculation zone610 is initiated by a flame kernel 630 that is produced by the igniter246 that is housed in the centerbody hub assembly 204. Additionally oralternatively, igniters 80 a (similar or identical to igniter 246 origniter 80) may also be employed near the dump plane 636 a.

The inlet ramp 212, which is optional, aids in increasing the size ofthe dump step 636 that occurs at the dump plane 636 a. In the particularexample provided, the inlet ramp 212 helps to create a relatively large90° dump step 636 at the transition between the inlet housing 200 andthe inlet of the combustor 40 a that serves to considerably improveflame propagation rates and the combustor's operability limits. Morespecifically, the dump step 636 creates a toroidal outer recirculationzone 640 along the combustor wall that is initially ignited by a flamekernel that is produced by the torch igniter 80 or the igniter(s) 246and/or 80 a (FIG. 4). The length of the outer recirculation zone 640 isa function of the height of the dump step 636 and the strength of theswirl number of the swirl vane pack 206. Generally speaking, for a givenconstant swirl number, the length, size and robustness of the outerrecirculation zone 640 are directly related to the height of the dumpstep. The inlet ramp 212 and its shape not only provide a means toeasily tune the flow height of the dump step 636 and the flow direction,but also increases the local flow velocities to thereby intensify theseparated shear layer turbulence and increases the rate of massentrainment of fuel into the shear layer. The ramp shape and reducedflow gap height also accelerates early merging of the shear layers 650and 600 of the outer recirculation zone 640 and the centralrecirculation zone 610, respectively, which is essential for combustorshaving a relatively short length. Those skilled in the art willappreciate that the shape of the ramp can be altered to change themaximum height and, therefore, the volume of the outer recirculationzone and the gaps between the outer and central recirculation zones.

Portions of the fuel that are dispensed by the fuel injectors 320, 340and 380 are employed to substantially fuel the central recirculationzone 610, while portions of the fuel that are dispensed by the fuelinjectors 230 of the wall injector assembly 208 are employed to fuelboth the outer recirculation zone 640 and fuel the central recirculationzone 610. Any portions of the fuel that is dispensed by the injectors230, 320, 340 and 380 that is not employed to fuel the central or outerrecirculation zones 610 and 640 is employed to generally fuel the maincore flow 700, which as those skilled in the art will appreciate,consists of the entire flow of combusting fuel and air except thecentral recirculation zone 610 and the outer recirculation zone 640. Thecentral recirculation zone 610 and the outer recirculation zone 640,once formed, contain a fixed trapped mass. An exchange of mass occursbetween each of the central and outer recirculation zones 610 and 640and the core flow 700, but there is no net change in mass for steadyflow conditions in either of the central and outer recirculation zones610 and 640.

As each of the injectors 320, 340 and 380 are coupled in a discretemanner to the fuel source 126, the amount of fuel that is dispensed bythe injectors 320, 340 and 380 may be tailored in a desired manner tofine tune flame stabilization and combustion performance duringthrottling. Accordingly, the injectors 320, 340 and 380 may beindependently controlled so as to provide a relatively wide range offlexibility to control combustor characteristics, depending on aparticular application.

The shear layers 650 and 600 of the outer recirculation zone 640 and thecentral recirculation zone 610 provide reduced velocity regions to holdthe flame, and maintain and propagate the combustion process. Morespecifically, the outer recirculation zone 640 and the centralrecirculation zone 610 provide flame stabilization and act as a robustignition source for the core flow 700 by supplying heat and recirculatedchemically reacting by-products, such as OH, H and O radicals, to themain fuel/air mixture of the combustor 40 a. In this regard, eachrecirculation zone carries the heat and chemically active species fromthe flame in the respective shear layer and recirculating flow volumeupstream where they act to ignite the fresh combustible fuel/air mixtureentering the shear layer to thereby provide a continuous pilot for thecore flow 700.

As noted above, the aft centerbody 244 of the swirl generator 30 may beconfigured in various different arrangements to achieve desired designparameters. For example, the aft centerbody 244 may be configured with achanneled aft bluff boat-tail 304 a as illustrated in FIG. 14. The aftbluff boat-tail 304 a is generally similar to the aft bluff boat-tail304 of FIG. 8, except that it includes a plurality of channels 800 thatare formed about the perimeter of the flow-effecting portion 362 a. Thechannels 800 are formed at an angle relative to the centerline of theaft bluff boat-tail 304 a that maintains the effective flow directionprovided by the swirl vane pack 206. Those skilled in the art willappreciate that other channels may be selected to control turbulenttransport and mixing including ones that are opposite of the tangentialdirection provided by the swirl vane pack. The ramp-like geometry of thechannels produces a spectrum of turbulence scales that enhances mixingto promote flame intensity and propagation from the centralrecirculation zone 610 into the core flow 700 (FIG. 13). Like the aftbluff boat-tail 304, the aft bluff boat-tail 304 a may include one ormore fuel injectors, or may have a “blank” configuration (i.e., aconfiguration without one or more fuel injectors).

In the embodiment of FIG. 15, the aft centerbody 244 b is illustrated tobe generally similar to the aft centerbody 244 of FIG. 9, except that itdoes not include a discrete bluff body. In this regard, the secondinjector ring 302 essentially forms a bluff body as the aft centerbody244 b terminates abruptly at the rear face of the second injector ring302.

The embodiment of FIGS. 16 and 17 is generally similar to that of FIG.15 except that the igniter 246 has been replaced with a fuel injector840, such as a simplex atomizer having, for example, a 100° spray angle.The fuel injector 840, like the previously discussed fuel injectors thatare housed in the aft centerbody 244, is individually coupled to a fuelconduit 252 so as to permit the fuel injector 840 to be selectivelydeployed. In this embodiment, the central recirculation zone is alsoignited by the flame kernel that is produced by the torch igniter 80and/or the igniter 80 a that are described above as initiatingcombustion in the outer recirculation zone.

Another embodiment is illustrated in FIG. 18 wherein the fuel injectorsin the wall of the inlet housing 200 f are replaced by a plurality ofcross-flow strut injectors 900. Each of the cross-flow strut injectors900 is swaged into the aft centerbody 244 f for structural support andcoupled in fluid connection to fuel conduits 906 that extend through theinlet housing 200 f. Each cross-flow strut injectors 900 has a pluralityof orifices 910 that promote atomization of the fuel flowingtherethrough. Additionally, this embodiment includes a channeled aftbluff boat-tail 304 f and a center-mount fuel injector 840.

The embodiment of FIGS. 19 and 20 provides a fuel injection scheme thatis very similar to that of the embodiment of FIG. 18. Instead ofcross-flow strut injectors, however, this embodiment utilizes aplurality of fuel injection sites 1000 a that are formed into a trailingedge 1002 g of at least a portion of the vanes 402 g of the swirl vanepack. The injection sites 1000 a are coupled in fluid connection to anassociated fuel conduit that extends through the conduit 120 (FIG. 4); aplurality of internal channels 1004 in the vanes 402 g serve to transmitthe fuel through the vanes 402 g to the injection sites 1000 a. Asillustrated in FIG. 20, each of the injection sites 1000 a is an orifice1006 that has an appropriate length to diameter ratio and which isformed into the trailing edge 1002 g at a predetermined angle relativeto an axis of the vane 402 g. Although the injection sites 1000 a areillustrated as being generally oriented in a downstream direction, thoseskilled in the art will appreciate that additionally or alternativelythe injection sites could also be skewed to the axis of the vane 402 g.Additionally or alternatively, the holes 1006 may be formed on a lateralsurface of the vanes 402 g to inject fuel in a desired direction (see,e.g., injection sites 1000 b and 1000 c in phantom in FIG. 20, which arealso formed with an appropriate orifice length to diameter ratio).Despite the complexity of the vane arrangement, this embodiment isadvantageous in that the exterior surfaces of the vanes 402 g form aneffective means for transferring heat from the air flow to the fuel inthe vanes 402 g which operates to cool the swirl vane pack as well as toincrease the temperature of the fuel that is injected, which tends toincrease the rate by which the fuel is mixed (i.e., improve atomization,decrease the size of the droplets in the fuel spray and directlyincrease the rate of droplet vaporization).

The embodiment of FIGS. 21 and 22 is generally similar to that of FIGS.19 and 20, except that an array or row of turbulator ramps 1050 areformed or mounted onto at least a portion of the vanes 402 h of theswirl vane pack 206 to further enhance mixing. The turbulator ramps 1050and the channels 1052 that are formed between each pair of turbulatorramps 1050 are employed to generate vortices that emanate from thetrailing edge 1002 h of the vanes 402 h; the vortices enhance turbulenttransport and provide highly controlled fine scale mixing. Like theprevious embodiment, a plurality of fuel injection sites 1000 h that areformed into a trailing edge 1002 h (i.e., into the tubulators 1050)which are coupled in fluid connection to an associated fuel conduit thatextends through the conduit 120 (FIG. 4); a plurality of integrallyformed channels 1002 h in each of the vanes 402 h serve to transmit thefuel through the vanes 402 h. Those skilled in the art will alsoappreciate that the turbulators 1050 may also be utilized in vaneconfigurations that do not inject fuel (i.e., in vanes without injectionsites formed therein).

The example of FIG. 23 is generally similar to that of FIG. 4, exceptthat the trailing edge 1002 i of the vanes 402 i includes a plurality ofscallops 1100 rather than turbulators. The scallops 1100 are illustratedto be formed in a uniform manner wherein the crest 1102 is relativelywider than the root 1104. Those skilled in the art will appreciate,however, that the scope of the present invention is not limited to anyparticular scallop pattern. Those skilled in the art will appreciate,too, that the vanes 402 i may also be configured with a plurality offuel injection sites in the manner described above for the embodimentsof FIGS. 19 through 22.

In the embodiment of FIGS. 24 and 24A, the inlet ramp 212 j isillustrated to be generally similar to the inlet ramp 212 of FIG. 4,except that a plurality of channels 1150 are formed about the perimeterof the inlet ramp 212 j. The channels 1150 are formed at a predeterminedangle relative to the longitudinal axis of the inlet housing 200 j andserve to enhance turbulent transport and fine scale mixing.

In the embodiment of FIG. 25, a plurality of circumferentially spacedapart fuel injection sites 1200 are formed about the circumference ofthe inlet ramp 212 k. The fuel injection sites 1200 are operable forinjecting fuel into the flow field which aids in flame stabilization andcommunication between the outer and central recirculation zones. Asthose skilled in the art will appreciate, the channels of the previousembodiment may additionally be incorporated into the inlet ramp 212 k.

Those skilled in the art will appreciate that the wall of the combustor40 a in an area proximate to the outer recirculation zone tends toabsorb a relatively large amount of heat during the combustion process.An optional quarl expansion 1250 may be provided as shown in FIG. 26 atthe dump step 636. The quart expansion 1250 is an annular element havinga generally triangular cross section; the quarl expansion 1250 isemployed to “fill” the backwards facing step at the dump plane such thatthe angle of the dump step 636 is reduced from 90°. The angle β of thequarl expansion 1250 may be varied in a known manner to affect the sizeof the central recirculation zone and the rate of heat transfer to thewall of the combustor 40 a and the inlet housing 200.

The embodiment of FIG. 27 illustrates that the configuration of thecenterbody assembly aft of the leading surface need not have theconfiguration of a right cylinder. In the particular embodimentillustrated, the portion of the centerbody assembly 236 m aft of theleading surface 272 m has a generally frusto-conical shape that issymmetrical about a longitudinal axis of the swirl generator 30 m. Thoseskilled in the art should also appreciate that the portion of thecenterbody assembly that is positioned aft of the leading surface may beother than conical (e.g., ogival). Those skilled in the art will alsorecognize that multiple fuel injection sites, similar to fuel injectors320, 340, 380 and/or 840 of FIGS. 8 and 16 could be incorporated intothe centerbody assembly 236 m.

The embodiment of FIG. 28 is generally similar to the embodiment of FIG.14 in that it includes two injection rings 1300 and 1302 that arepositioned forwardly of the aft bluff boat-tail 304 a. This embodimentdiffers from the embodiment of FIG. 14 in that the injection rings 1300and 1302 are configured in a manner that is generally similar to that ofthe first injection ring 300 and a third injection ring 1304 is coupledto the aft end of the aft bluff boat-tail 304 a. The injection ring 1304is configured generally similar to that of the second injection ring 302discussed above (i.e., includes fuel injectors and threadably engagesthe threaded portion 336 of the igniter 246). Additionally, theinjection ring 1304 includes a plurality of optional grooves or channels1310 that may be continuous with the grooves or channels of the bluffboat-tail body 800 which produces a spectrum of turbulent scales thatenhance fuel and air transport and fine scale mixing to promote flameintensity and propagation from the central recirculation zone 610 intothe core flow 700. As those skilled in the art will appreciate, theinjection rings 1300, 1302 and/or 1304 may be “blank” and/or may includegrooves or channels 1310 for producing fine scale turbulence.Furthermore, the injection ring 1304 may be configured with an aftfacing fuel injector such as that which is shown in FIGS. 16 and 17.

Ramjet Powered Applications

While the swirl generator of the present invention has been illustratedand described thus far as being a component of a lift thrust augmentor,those skilled in the art will appreciate that the invention, in itsbroader aspects, may be utilized in diverse other applications. In FIGS.29 and 30, for example, the swirl generator 30 is illustrated inconjunction with a ramjet missile 2000.

In this example, the ramjet missile 2000 includes a forebody 2002, fins2004, a booster engine 2006 and a ramjet engine 2010 having an air inlet2012, the swirl generator 30 and a ramjet combustor/nozzle 2014. Theforebody 2002 conventionally houses the payload (not shown), the fuel(not shown), batteries (not shown) and the control portion (not shown)of the ramjet missile 2000, while the fins 2004 conventionally stabilizeand guide the ramjet missile 2000. The air inlet 2012 includes a movableor consumable port cover (not shown) that is selectively operable forsealing the air inlet 2012 and the swirl generator during the operationof the rocket booster engine 2006. In the example provided, the rocketbooster engine 2006 includes a solid propellant 2018 that burns during aboost phase of the missile's operation; hot combustion by-products areexpelled from the nozzle 2020 of the booster engine 2006 to generatethrust.

Subsequent to the boost phase of the missile's operation, the boosterengine 2006 of the exemplary ramjet missile illustrated is ejected andthe movable port cover is also ejected or consumed so as to permit airto flow into the air inlet 2012 so that the task of propulsion mayswitch from the rocket booster engine 2006 to the ramjet engine 2010.The speed of the missile 2000 and the configuration of the air inlet2012 cooperate to induce an airflow 2026 through the air inlet 2012 thatis directed toward the swirl generator 30. Alternatively, as illustratedin FIG. 30A, a plurality of flow guide vanes 96 a (similar to the flowguide vanes 96 in the elbow 60) may be employed in the air inlet 2012 toprovide an axisymmetric (i.e., uniform and axial) airflow to the swirlgenerator 30. Those skilled in the art will recognize that a chin inletmay be used followed by an annular air transfer duct that acts as anisolator and carries the air aft to the swirl generator 30 and thecombustor of the ramjet combustor/nozzle 2014. In this case the airtransfer duct will typically be S-shaped and may require guide vanes tostraighten the flow as previously described. The swirl generator 30 isemployed to generate a turbulent flowfield and to inject fuel therein inthe manner described above. As in the example of the lift thrustaugmentor, the swirl generator 30 operates to effect both an outerrecirculation zone (proximate the dump step 2030 at the transitionbetween the inlet housing 2032 and the inlet of the combustor/nozzle2014), as well as a central recirculation zone (which is anchored by theaft end of the aft centerbody assembly 244).

Integration of the swirl generator 30 into the ramjet missile 2000permits significant reductions to the L/D ratio of the combustor 2014 aand substantial reductions in the overall length and weight of theramjet missile 2000. Furthermore, the shortened combustor lengthprovided by the swirl generator 30 allows the booster engine 2006 to beseparately packaged and thus be ejectable as the propulsion switchesfrom the booster engine 2006 to the ramjet engine 2010. A shorter andlighter weight missile, due to the swirl generator 30, will offersignificant maneuverability advantages over longer and/or heaviermissiles due to a shorter turning radius capability. The CoSATtechnology may also require a smaller booster due to ramjet take-overoccurring at a lower Mach number and hence offer additional rangecapability and/or further improved agility.

Another application is illustrated in FIG. 31 wherein the swirlgenerator 30 n is illustrated in conjunction with a ramshell 2300. Theramshell 2300 is a gun-launched, spin-stabilized projectile that employsthe above-described ramjet technology to accelerate the ramshell 2300 toa velocity of about Mach 4 to about Mach 6 to extend the projectilerange, minimize the time to target and maximize the penetrationcapability of the projectile. The ramshell 2300 includes a housing 2302,a projectile 2304, a plurality of inlet struts 2306, the swirl generator30 n and a combustor/nozzle portion 2308.

The housing 2302 is a hollow shell that is inwardly tapered at it'sfront end to define an air inlet 2310. The inlet struts 2306 are fixedlycoupled to the interior of the housing 2302 and to the projectile 2304to centrally mount the projectile 2304 in a forward portion of thehousing 2302. As the ramshell 2300 is spin-stabilized, the inlet struts2306 have a spiral shape to maintain alignment with the incoming airflow. The air flow is compressed through the inlet section 2310 a andshocked to subsonic velocities near the aft end of the inlet struts2306. While the projectile 2304 is illustrated as being a solid metallicrod, those skilled in the art will appreciate that any form of payload,including an explosive charge, may be employed in the alternative.

The swirl generator 30 n is mounted on the aft end of the projectile2304 and the swirl vane pack 206 serves to support the housing 2302 aftof the inlet struts 2306. Fuel injection is somewhat different from thatof the swirl generator 30 of FIG. 4 in that the primary purposes of theswirl generator 30 n are to augment the central recirculation zone(similar to the central recirculation zone 610 of FIG. 13) and tocontrol the rate of mixing in the shear layer above the centralrecirculation zone and to control the rate of flame propagation into thecore flow. Accordingly, wall injection is not employed in thisembodiment, and the fuel injectors 2320 in the centerbody assembly 236 nare fueled by a reservoir 2330 that is internal to the aft centerbodyassembly 244 n. The reservoir 2330 includes a pressurized bladder 2332that surrounds the fuel 2334 to maintain the pressure of the fuel 2334at sufficient levels during the operation of the ramshell 2300. Thecentrifugal force of the rotating fuel 2334 in the reservoir 2330 keepsthe cooler, high density liquid fuel against the outer perimeter of thereservoir 2330 to assist in thermal protection of the combustor/nozzleportion 2308.

Fuel injection in the ramshell 2300 is preferably designed to maintain asomewhat fuel-rich condition in the central recirculation zone. As themain propulsive combustion initiates in the shear layer above thecentral recirculation zone, the level of mixing and heat release iscontrolled through the design of the swirl generator 30 n so that onlythe air flow in the vicinity of the shear layer participates incombustion. Operation in this manner leaves the outer region near theinterior side of the housing 2302 relatively cooler and protects thehousing 2302 from the high heat flux near the throat of thecombustor/nozzle portion 2308, before mixing of the hot combusting gaseswith the outermost air is complete.

Combined-Cycle Applications

FIGS. 32 and 33 illustrate yet another application of the swirlgenerator of the present invention. In this example, a swirl-augmentedcombined cycle engine 2400 is illustrated to include a core turbojetengine 2402, a plurality of ramjet engines 2404 that surround the coreturbojet engine 2402 and a flow controller 2406. The core turbojetengine 2402 conventionally includes a low pressure compressor 2410, ahigh pressure compressor 2412, combustors 2414, an air bypass 2416 and ahigh pressure turbine 2418. As those skilled in the art will appreciate,the core turbojet engine 2402 may optionally include an afterburner 2402a and a variable area nozzle 2402 b. Although the afterburner 2402 a isillustrated to be a conventional afterburner having a fuel spray ringand a concentric V-gutter flameholder ring, those skilled in the artwill appreciate the that the afterburner 2402 a may alternatively beconfigured in the manner illustrated in FIG. 41 and discussed in detail,below.

The ramjet engines 2404 are configured in a manner that is similar tothe ramjet missile of FIGS. 29 and 30. Briefly, each of the ramjetengines 2404 includes an air inlet 2420, a swirl generator 30 and aramjet combustor/nozzle 2430.

The flow controller 2406 is coupled to the core turbojet engine 2402 andincludes a forward movable element or diverter 2440, which is employedto selectively control the intake of air into the core turbojet engine2402 and the ramjet engines 2404, and an aft movable element or diverter2442, which is employed to selectively close off the outlet of the coreturbojet engine 2402 and the ramjet engines 2404. In the particularexample provided, the forward and aft movable elements 2440 and 2442 arehingedly mounted to the housing 2450 of the core turbojet engine 2402and pivotable between a first condition (illustrated in broken line),which closes off the air inlet 2420 and combustor/nozzle 2430,respectively, of each ramjet engine 2404, and a second condition(illustrated in solid line), which closes off the intake side of the lowpressure compressor 2410 and the outlet of the high pressure turbine2418, respectively. The forward and aft movable elements 2440 and 2442may be moved through any of the various conventionally known means,including hydraulic actuators (not shown).

The core turbojet engine 2402 produces all of the propulsive power thatis output by the swirl-augmented combined cycle engine 2400 from zerovelocity through a predetermined transition-in velocity of, for example,at about Mach 2. Therefore, the forward and aft movable elements 2440and 2442 are maintained in the first condition at speeds below thepredetermined transition-in velocity.

At the predetermined transition-in velocity, the ramjet engines 2404 areactivated to provide additional thrust. Flow entering the ramjet engines2404 is subjected to additional ramjet compression 2460 and is furthercompressed to subsonic speeds in a transfer duct/shock isolator 2462.The air flow enters the swirl generator 30 and is converted into ahighly turbulent flowfield into which fuel is injected in the mannerdescribed above. As the core turbojet engine 2402 is also producingthrust, the forward and aft movable elements 2440 and 2442 aremaintained in a position between the first and second conditions.Additionally or alternatively, thrust augmentation by one or more of theramjet engines 2404 may be accomplished via a bleed-burn process whereinair is tapped-off the high pressure compressor 2412, routed to theramjet engines 2404 and burnt with added fuel (up to stoichiometricconditions) in the ramjet engines 2404. When the bleed-burn process isto be initiated, a valve 2463 is opened to permit air to flow through aduct 2464 into the ramjet 2404. Those skilled in the art will appreciatethat a plurality of guide vanes 96 b, similar to guide vanes 96discussed above, may be employed to provide a smooth, low loss entry ofthe bleed air into the ramjet engine 2404.

When air speed reaches a predetermined ramjet takeover velocity of, forexample, about Mach 3 to about Mach 4, the forward and aft movableelements 2440 and 2442 are positioned in the second condition and thrustproduction shifts entirely to the ramjet engines 2404. The swirl ramjets20 provide the required thrust from about Mach 3 to the cruise conditionat speeds of up to approximately Mach 6.

As those skilled in the art will appreciate, the position of the forwardand aft movable elements 2440 and 2442 may be controlled in response toflow sensors (not shown) in a selective manner to thereby affect theamount of air that is directed to the core turbojet engine 2402 and theramjet engines 2404. Alternatively, the forward and aft movable elements2440 and 2442 may be controlled such that they move continuously fromthe first condition to the second condition at a predetermined rate uponthe sensing of an air speed equivalent to the predeterminedtransition-in velocity or other event which would prompt the transitionfrom one propulsion mode to another. By incorporating the swirlgenerator invention into the ramjet engine, this combined cycle engineconcept can significantly reduce weight and size, yet provide highperformance of the combustor and swirl ramjet concepts compared to otherknown turbine-based combined cycle engines using conventional ramjetsystems. It also reduces the ramjet hot section length, thus reducingcooling requirements.

One unique feature of this concept is the aft-end valving that isaccomplished by the aft movable element 2442. The shape of the aftmovable element 2442 is such that when positioned in the secondcondition, the aft movable element 2442 seals-off the aft end of thecore turbojet engine 2402 and extends rearwardly in a manner wherein thesurface 2442 a of the aft movable element 2442 defines one of thesurfaces of the nozzle portion of the ramjet combustor/nozzle 2430.Conversely, when the aft movable element 2442 is positioned in the firstposition, its surface 2442 b defines a portion of an expansion nozzlefor the core turbojet engine 2402.

Another swirl-augmented combined cycle engine 2400 a is illustrated inFIGS. 34 and 35. The swirl-augmented combined cycle engine 2400 a issimilar to the swirl-augmented combined cycle engine 2400 of FIGS. 32and 33 in that it employs turbojet engines 2402, ramjet engines 2404 aand a flow controller 2406 a, which selectively controls the input ofair to the turbojet engine 2402 and the ramjet engine 2404 a. Theswirl-augmented combined cycle engine 2400 a, however, is globallyrectangular, segregated into a plurality of engine cells 2500, with eachengine cell 2500 including a turbojet engine 2402 a, a ramjet engine2404 a and a flow controller 2406 a. Operation of each engine cell 2500is identical to the operation of the swirl-augmented combined cycleengine 2400 of FIGS. 32 and 33 and as such, need not be described indetail. The plurality of engine cells 2500 are operated in a manner suchthat propulsion is regulated between the turbojet engines 2402 and theramjet engines 2404 a in a uniform manner across the engine cells 2500(i.e., transition from turbojet propulsion to ramjet propulsion issubstantially simultaneous across all of the engine cells 2500).

A third swirl-augmented combined cycle engine 2400 b is illustrated inFIG. 35A. The swirl-augmented combined cycle engine 2400 b is a variantof the two previously described swirl-augmented combined cycle engineconfigurations in FIGS. 32 and 34, with one major difference being thatthe core engine 2402 b is coaxial with the ramjet engine 2404 b. In theexample provided, the core engine 2402 b is a conventional gas turbineengine that features a coaxial afterburner 5020 having a swirl generator30 r, thus replacing the long diffuser cone, one or more fuel sprayrings and one or more concentric V-gutter flameholder rings.

The key features of the swirl generator include a variable angle swirlvane pack 206 r, a centerbody assembly 236 r, which includes acollapsible centerbody cone 5022, a burner 5024, which employs a quarlstep 5026, an array of first fuel injectors 5028, which are integrated(e.g., embedded) into the base of the vanes 402 r of the swirl vane pack206 r for main afterburning, an array of second fuel injectors 5030(illustrated as injection orifices in the particular example shown) thatare located on the aft centerbody assembly 244 r for ignition andpiloting the afterburning, one or more igniters (not shown) that arelocated in the aft end or base of the aft centerbody assembly 244 rand/or in the recess of the quarl step 5026 and a variable area nozzle5010.

The swirl-augmented combined cycle engine 2400 b operates in a similarmanner to those combined cycle engine concepts already described andtherefore will not be discussed in detail other than to note that theswirl generator 30 r is employed for both the turbojet and ramjet enginecycles and therefore allows for a reduction in the overall length of theturbojet.

In operation, the combined cycle engine 2400 b employs a translatingspike 5050 and an inner turbojet cowl 5060. The translating spike 5050is employed to control the shock-on-lip condition during supersonicspeeds for both turbojet and ramjet operation, while the translatingturbojet cowl 5060 cooperates with the translating spike 5050 to controlthe flow split during turbojet and ramjet mode operation (i.e., theportion of the intake air flow that is directed to the core turbojetengine 2402 b and the ramjet engine 2404 b). Although the forwardportion of the translating spike 5050 is shown with a single cone angle,those skilled in the art will recognize that multiple cone angles may beemployed to approximate an isentropic spike to thereby minimize totalpressure losses generated by inlet shocks.

During the take-over of propulsion by the ramjet engine 2404 b, thetranslating spike 5050 is moved forwardly toward the inner turbojet cowl5060 so as to close off the turbojet air intake 5084 and shift the airflow to the outer cowl inlet 5080 and into the air transferduct/isolator 5070. The valve 5040 is positioned in the outer airtransfer duct/isolator 5070 in an open condition to allow air to flowdirected into the swirl generator 30 r and through the nozzle 5010. Inthis condition, the upstream portion of the turbine air bypass duct 5090is closed off to prevent feedback and resonance using the same valve5040 or an alternate valve 5045. Those skilled in the art willappreciate that the valve 5040 is not required if the core turbojetengine 2402 b lacks an air bypass duct 5090. The variable area nozzle5010 is also repositioned during mode transition (i.e., the transitionfrom turbojet propulsion to ramjet propulsion).

This swirl-augmented combined cycle engine 2400 b allows very compactengine packaging to reduce weight and length, yet provides highperformance compared to known turbine based combined cycle engines thatutilize conventional gas turbine afterburners and ramjet systems. Theswirl generator 30 r/nozzle, which serves as the afterburner for the gasturbine engine and ramjet engine, also reduces the traditional ramjetengine hot section length and in turn reduces cooling requirements tomaintain structural and thermal integrity of the hardware.

Rocket-Based Combined Cycle

FIGS. 36 and 37 illustrate yet another application of the swirlgenerator of the present invention. In this embodiment, a rocket-basedcombined cycle engine 4000 is illustrated to include a housing 4002, oneor more rocket engines 4004, a ramjet engine 4006 and a nozzle 4008. Thehousing 4002 houses the rocket engines 4004 and the ramjet engine 4006and defines an air inlet 4020. The rocket engines 4004, which may becoupled to the housing 4002 such that they are located in the dump step4022 (or quarl surface) and/or inside the aft end of the aft centerbodyassembly 244 p, may employ a liquid, slurry or solid fuel, dependingupon the application and considerations for the altitude, range andspeed that are mandated by the mission. The ramjet engine 4006 includesa swirl generator 30 p which is generally similar to the swirl generator30, except for the aforementioned rocket engine 4004 that is mounted toaft centerbody assembly 244 p.

The rocket engines 4004 provide low speed thrust and additionally serveto pump air into the air inlet 4020. Air flowing through the air inlet4020 is converted into a highly turbulent flow field into which fuel isinjected and mixed (via the swirl generator 30 p) in the mannerdescribed in detail above. In this regard, the air flowing through theair inlet is employed in an afterburning operation by the ramjet engine4006 to augment the thrust that is generated by the rocket engines 4004at all speeds. The pumping action is a result of the momentum transferfrom the high velocity rocket exhaust and the entrained ambient air. Themomentum transfer is the result of the turbulent exchange through theshear layers separating the exhaust of each rocket engine 4004 and theentrained air. Alternatively, the rocket engines 4004 may be used torapidly accelerate the rocket-based combined cycle engine 4000 above apredetermined speed threshold after which propulsion is transitioned tothe ramjet engine 4006.

Those skilled in the art will appreciate that a forward flap or diverter(not shown) may be employed to close-off the air inlet 4020 during lowspeed operation of the rocket-based combined cycle engine 4000 to effectpure rocket thrust generation up to a predetermined speed thresholdafter which propulsion is transitioned to the ramjet engine 4006. Thismode of operation produces higher ramjet combustor pressures andassociated thrust without the occurrence of backflow through the airinlet 4020 at lower speeds.

For optimum thrust in any mode of operation, the nozzle 4008 preferablyincludes a variable area throat 4030. The variable area throat 4030 isselectably configured to match the flow rate and back-pressurerequirements of the rocket-based combined cycle engine 4000 for maximumand efficient thrust generation. Those skilled in the art willappreciate, however, that other nozzle throat concepts may be employedin the alternative, including consumable throat inserts, frangiblethroat inserts and ejectable throat inserts.

With additional reference to FIGS. 38 and 39, an exemplary variable areathroat 4030 is illustrated to include a plurality of throat closureelements 4032 that are rotatable in the housing 4002 through an angle ofabout 90° between an open position, which is illustrated in FIGS. 37 and38, and a closed position, which is illustrated in FIG. 39. Althoughonly six elements are shown, those skilled in the art will appreciatethat the number of throat closure elements 4032 may be varied tocoordinate with the particular upstream geometry of the a rocket-basedcombined cycle engine 4000. In the particular example illustrated, gaps4034 are aligned to the six upstream rocket engines 4004 in the lowspeed mode to minimize erosion of the throat closure elements 4032during the operation of the rocket engines 4004. When the throat closureelements 4032 are positioned in the closed position during the operationof the ramjet engine 4006, the area of the throat is substantiallyreduced.

In the embodiment illustrated, the throat closure elements 4032 rotateabout an axis on a plane or facet on the inner surface of the housing4002. The operational mechanism for rotating the throat closure elements4032 may be housed in the housing 4002 or mounted on an adjacentstructure (e.g., fins) to which the rocket-based combined cycle engine4000 is mounted. Preferably, the throat closure elements 4032 areoperated in opposed pairs so as to minimize rotational torques on therocket-based combined cycle engine 4000 when the throat closure elements4032 are moved between the open and closed positions.

When the throat closure elements 4032 are positioned in the closedposition, the throat closure elements 4032 cooperate to provide thethroat with an approximately circular shape; the extent to which thethroat is circular is dependent upon the number of throat closureelements 4032 that are employed and whether or not the edges of thethroat closure elements 4032 are contoured.

During the operation of the rocket-based combined cycle engine 4000,compressed air enters the air inlet 4020 and is directed to the swirlgenerator 30 p. The air inlet 4020 also functions as an isolator atsupersonic flight speeds where the air is further compressed and broughtto subsonic speeds prior to being directed into the swirl generator 30p. The length of the air inlet duct 4020 is dictated by packagingrequirements including fuel, propellants, warhead type (for missileapplications), plumbing, controller(s), actuators and batteries. Theminimum length of the air inlet duct 4020 is dictated by the isolationrequirements that are necessitated during supersonic flight speeds.

During the combined operation of the rocket engines 4004 and the ramjetengine 4006, the swirl generator 30 p functions to augment core flowmixing where flame stabilization is achieved in the recirculation zonesin the backward facing areas between the exhaust nozzles 4004 a of therocket engines 4004 that are mounted in the outer step and/or an annularlip region at the end of the aft bluff boat-tail 304 p. Special ignitersare not required since the hot rocket exhaust will serve to ignite thefuel/air mixture for afterburning and ramjet operation. In addition,fuel and/or rocket propellant may be continuously bled through theotherwise idle rocket engines to help cool them and to prevent back flowof the ramjet's hot combustion by-products. The total engine flow passesthrough the variable area throat 4030 and is expelled to the atmosphere.Although the primary application anticipated for this technology ismissile propulsion, those skilled in the art will appreciate that therocket-based combined cycle engine 4000 may also be employed foraircraft propulsion where reduced weight and complexity would bedesired.

Afterburning Turbojet Engine Applications

Another application of the swirl generator of the present invention isshown in FIG. 41, which illustrates the retrofitting of a compact swirlafterburner 5020 for a conventional afterburner 5000 of the military gasturbine engine 5002 that is shown in FIG. 40. Briefly, the military gasturbine engine 5002, which may be a turbojet engine or a turbofanengine, includes a coaxially-mounted afterburner 5000 having a diffusertailcone 5004 with one or more fuel spray rings 5006, one or moreconcentric V-gutter flameholder rings 5008 and a variable area nozzle5010. The variable area nozzle 5010 is fully opened for afterburningoperation and is reduced for non-afterburning operation.

Returning to FIG. 41, retrofit of the military gas turbine engine 5002entails the substitution of afterburner 5020 for the conventionalafterburner 5000 (FIG. 40). The afterburner 5020 includes swirlgenerator 30 r having a variable-angle swirl vane pack 206 r, acenterbody assembly 236 r, which has a collapsible centerbody cone 5022,an expanding burner 5024, which has a quarl step 5026, an array of fuelinjectors 5028 that are embedded into the base of the vanes 402 r formain afterburning, an array of circumferentially spaced apart fuelinjectors 5030 (illustrated as injection orifices in the particularexample illustrated) located on the aft centerbody assembly 244 r forignition and piloting the afterburning, and one or more igniters (notshown) that are located in the aft end or base of the aft centerbodyassembly 244 r and/or in the recess of the quarl step 5026.

In order to maximize the benefits of the swirl augmentation provided bythe swirl generator 30 r, attachment of the swirl generator 30 r shouldbe as close as possible to the turbine exit plane. Accordingly, thelength of the conical diffuser (i.e., the collapsible centerbody cone5022) can be shortened relative to the embodiment of FIG. 40.

The hot gases, which consist mostly of air exiting the turbine andrelatively cold air from the bypass fan of the main engine, enter theswirl generator 30 r where they are swirled and the streams are mixed toform a highly turbulent, three-dimensional flowfield. The fuel that isinjected into this high shear stress-laden swirling flow is rapidlyatomized and mixed. Atomization and mixing are controlled by a noveldesign of the swirl generator 30 r.

The swirling mixture of the afterburner fuel, hot turbine gases andcolder bypass fan air are slowed down across the quarl step 5026 as theflow enters the combustor 5024, and creates a central recirculation zoneand an outer recirculation zone similar to the central recirculationzone 610 and outer recirculation zone 640 of FIG. 13. The centralrecirculation zone is governed by the combined effects of the swirlstrength (a characteristic of the variable-angle swirl vane pack 206 r)and the blunt aft end of the aft centerbody assembly 244 r. The outerrecirculation zone is created by separation of the fuel/air mixture asit flows over the quarl step 5026. Combustion in the afterburner 5020 isvery robust, stable and highly efficient such that the energetic, hightemperature byproducts of the combustion event are expanded through thevariable area nozzle 5010 to provide high levels of thrust.

During non-afterburning operation, the swirl generator 30 r serves as achannel between the main engine and the variable area nozzle 5010. Toavoid significant pressure losses due to the presence of the vanes 402r, the variable-angle swirl vane pack 206 r is controlled such that theangle of the vanes 402 r is changed to 0° so as to remove the swirl fromthe flow and thereby maintain the axial character of exhaust flow. Vanes402 r having a flat profile are presently preferred. As an alternativeto the variable angle swirl vane pack 206 r, a two-position-swirl vanepack (not shown) may also be employed. Also during non-afterburningoperation, the collapsible centerbody cone 5022 that is attached to theaft centerbody 244 r is extended to create a flowfield with relativelygreater aerodynamic efficiency and relatively lower pressure losses.

With reference to FIG. 41A, a two-position, retractable centerbodyaft-cone 5022B is employed for mode transition. The retractablecenterbody aft-cone 5022B is fully extended rearward, as is depicted inthe portion of the figure above the centerline, during non-afterburningoperation to maintain low pressure loss by keeping the flow attached tothe aft cone, and is fully retracted forward, as is depicted in theportion of the figure below the centerline, during afterburningoperation to provide flow separation with a robust central recirculationzone that is required for flameholding and rapid flame spreading. Thehousing of the centerbody 5022A has an annular thickness (i.e., definesan annular wall) that contains the manifolds for the fuel injectionsites 5028. Various means may be employed to actuate (i.e., extend andretract) the retractable centerbody aft-cone 5022B, such as internalhydraulic or pneumatic actuators that may, for example, be fuel driven.As another alternative, the retractable centerbody aft-cone 5022B may beactuated via a conventional and well-known jackscrew type actuator.Support and guidance for the retractable centerbody aft-cone 5022B maybe provided by the actuator and the housing of the centerbody 5022A. Inthe retracted position, although a portion of the housing of thecenterbody 5022A is exposed when the retractable centerbody aft-cone5022B is retracted, the fuel flowing through it to the fuel injectionsites 5028 functions as a coolant which cools the housing of thecenterbody 5022A.

Because the afterburner 5020 is able to operate at flamespreadingvelocities that are over four times greater than those attainable by theconventional afterburner 5000, combustion in the afterburner 5020 iscompleted in a considerably shorter distance, and therefore it becomescompact, lighter in weight and more fuel efficient than the conventionalafterburners. Additionally, no aero-intrusive instream flameholders 5008of FIG. 40 are required, because the flame stabilization and propagationprocesses are controlled by the aerodynamics of the swirling flowfield.No aero-intrusive fuel injection rings 5006 of FIG. 40 are neededeither, because the fuel is injected from the trailing edges 5028 of theswirl vanes and the centerbody 5030. The long tail cone 5004 iseliminated and replaced with a short centerbody 236 r having anextendable and retractable tapered cone 5022, and variable angle swirlvanes 206 r to accommodate afterburning and non-afterburning modes ofoperation in order to maximize thrust output at all operatingconditions.

The thermal control of the swirl-augmented afterburner could beperformed using known combustor technology methods. These techniqueswould include: fuel scheduling to minimize heat flux to the walls;bypass air cooling, bleed, and film cooling to reduce the temperature ofwall materials; and the use of high temperature alloys and materials towithstand the afterburner operating temperatures. Ceramic matrix andother high temperature/refractory materials can be used in localizedzones. In addition, fuel injector faces and possibly portions of theexposed centerbody surfaces may be fuel cooled. A specific design wouldutilize multiple approaches to minimize thermal issues and provideincreased service life at the lowest cost.

While the invention has been described in the specification andillustrated in the drawings with reference to various preferredembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention asdefined in the claims. In addition, many modifications may be made toadapt a particular situation or material to the teachings of theinvention without departing from the essential scope thereof. Therefore,it is intended that the invention not be limited to the particularembodiment illustrated by the drawings and described in thespecification as the best mode presently contemplated for carrying outthis invention, but that the invention will include any embodimentsfalling within the foregoing description and the appended claims.

1. An afterburner apparatus comprising: an expanding burner having aninlet; a swirl generator that is coupled to the inlet of the burner, theswirl generator being operable for converting an oxidizer flow into athree-dimensional flowfield that includes a substantial tangentialvelocity component, the swirl generator including a flow defining meansand a fueling means, the flow defining means being operable foreffecting both an outer recirculation zone and a central recirculationzone in the burner, the outer recirculation zone being toroidal inshape, the central recirculation zone being disposed inwardly of theouter recirculation zone, the fueling means being operable for fuelingthe outer and central recirculation zones; and a variable area nozzlereceiving combustion byproducts produced during combustion in the burnerand producing propulsive thrust in response thereto; wherein heat andthe combustion byproducts produced during combustion are carriedupstream by the outer and central recirculation zones where the heat andcombustion byproducts are employed to continuously ignite a combustiblefuel/oxidizer mixture in a shear layer adjacent each of the outer andcentral recirculation zones.
 2. The afterburner apparatus of claim 1,wherein the flow defining means includes a swirl vane pack having aplurality of vanes and wherein the vanes are configured to selectivelyprovide the swirl vane pack with a swirl number that is less than about2.0.
 3. The afterburner apparatus of claim 2, wherein the swirl numberof the swirl vane pack is about 0.4 to about 1.2.
 4. The afterburnerapparatus of claim 2, wherein the vanes have a flat profile.
 5. Theafterburner apparatus of claim 1, wherein the plurality of fuelinjectors include a plurality of fuel injection sites that are formedinto at least a portion of the vanes of the swirl vane pack.
 6. Theafterburner apparatus of claim 5, wherein each vane includes a trailingedge and a lateral surface and wherein the fuel injection sites on agiven vane are formed into at least one of the trailing edge and thelateral surface.
 7. The afterburner apparatus of claim 1, wherein thecenterbody assembly includes an extendable centerbody cone.
 8. Theafterburner apparatus of claim 1, wherein the inlet of the burnerincludes a quarl expansion.
 9. The afterburner apparatus of claim 1,wherein an inlet ramp is formed onto an inlet housing adjacent a dumpstep.
 10. The afterburner apparatus of claim 9, wherein a plurality ofcircumferentially spaced apart injection sites are formed into the inletramp, the injection sites comprising at least a portion of the fuelinjectors.